It's not as easy as it looks!

A project log for Arduino Nextion Android Midi Valve Guitar Amp

Control a Marshall JCM800 2204 style guitar amp using touch screens, midi foot pedals and an Android App

Paul BurfordPaul Burford 09/08/2019 at 15:450 Comments

It took about three months to design my first PCB. I made the fatal design error of trying to fit it all into the smallest space possible. So, I designed a single PCB using the few rules that I knew and I placed the order from JLC in China.

I fully populated the board even though the programming of the arduino was far from finished. The interference from the Arduino was huge. The hum, or should I say buzz, was like a chainsaw. Whilst the amplifier itself was working, there was no way that I could live with the background noise. I went back to the drawing board and redesigned the PCB. This time I didn't include the wiring for the Arduino. I was determined just to get the amplifier side of things working. PCB rev 2 turned up a month later...

The bottom half of this PCB was similar in layout to the Marshall JCM800 PCB, albeit with a lot of spaces for optoisolators instead of wires going to potentiometers. I started off with pots loose on floating wires. The amp breathed it's first breath... but optoisolators replacing the gain pot would have to be moved. They were creating a lot of hum. Relocating them an inch away from their current location (in any direction!) solved that problem. Time to think about the PCB that would house the Arduino. Perhaps it could house the gain pot optoisolators as well.